Preheat oven to 350 degrees. Line a 9x13” baking pan with foil and spray with cooking spray.
Place almond paste in a food processor and pulse until the mixture becomes a fine crumb, just a few seconds.
Place butter and 1 cup of the almond paste crumbs in the bowl of an electric mixer fitted with a paddle attachment. Add sugar and beat on medium speed until fluffy. Add flour slowly and mix until mixture becomes together (it will be crumbly). Press in an even layer into the prepared pan. Bake for 15 minutes.
Place the sweetened condensed milk and remaining almond paste in a medium bowl. Microwave for 30 seconds and stir to combine.
When the crust comes out of the oven, sprinkle the white chocolate chips and sliced almonds over the top. Pour the sweetened condensed milk mixture over the top and spread evenly as gently as possible so as not to mix up the toppings.
Bake for 20 minutes, or until the edges begin to brown. Cool completely before cutting into bars.