Combine the lukewarm water, 1 tablespoon of sugar, and yeast in a bowl. Whisk to dissolve the yeast. Leave for 5-10 minutes
In a large mixing bowl, combine the flour, salt, baking powder, and the remaining sugar.
Add in buttermilk, egg, melted butter, vanilla, and the yeast mixture. Stir until incorporated. Mix using a dough hook on your mixer or by hand. Knead on low-medium speed for about 5 minutes. By hand, knead the dough for about 10 minutes until smooth.
Transfer the dough to a lightly greased bowl, cover with plastic wrap, and allow to proof in a warm, draft-free place for about 1 hour or until doubled in size.
Cut out 16 squares of parchment paper.
Punch the dough and turn it out onto a lightly floured surface.
Use a rolling pin to roll to about 1/2" thickness, and use a donut cutter to cut out donuts. Place each on the prepared squares of parchment paper. Cover lightly with plastic wrap or a towel.
Allow the donuts to proof at room temperature for 30-45 minutes or until almost doubled in size. Heat 2 inches of oil in a heavy pot (cast iron is best) to 330-350°F. To fry donuts, drop 2-3 at a time and allow to become golden before turning to the other side, about 2 minutes per side. Remove donuts from the oil and place on a tray lined with paper towels.
To decorate
Toast almond slices in a pan. Stir occasionally to avoid burning. For the white chocolate glaze, heat the cream in a microwave-safe bowl until the sides are bubbly, about 1-2 minutes. Place the white chocolate chips into a medium bowl, pour the hot cream over. Stir until smooth. Dip each donut into the glaze and top with almond slices.